Transcript File

Exploring the World of Network
Models
LETS
DO
THIS!
Content based on: Managing and Troubleshooting Networks, Mike Meyers, Fourth Edition
GOALS FOR FIRST WEEK:
 Describe how models such as the OSI seven-layer model and the TCP/IP
model help technicians understand and troubleshoot networks
 Explain the major functions of network hardware with the OSI sevenlayer model
 Describe the major functions of networks with the TCP/IP model
NETWORK MODELS – WHY AND WHAT?:
• Why use a model to describe how a network
works?
• Networking is complicated!!
• Communicate with others about what is happening and where it
is happening
• Two well accepted Network Models:
• The Open Systems Interconnect (OSI) model
• The Transmission Control Protocol/Internet Protocol (TCP/IP)
model
• Overall, these models provide:
• A powerful tool for diagnosing
problems
• A common language to describe
networks
LAYERS AND PROTOCOLS
• Each model is made up of several layers
• There are specific protocols (rules, regulations,
standards) for each layer
• THE OSI model is the most widely used because
its very specific about the layers and their
functions
• Let’s break down the layers through an
example…
SO WHAT DOES THIS MEAN?
THE OSI SEVEN-LAYER MODEL IN ACTION
• WWU Daily Operations Example:
• One of the workers has just completed a new
employee handbook in MS Word
• She needs to transfer the Word document to the other
worker for review
• So what are her options to transfer the
Word document?:
• Flash Drive
• Transfer file using the network
• Let’s break down how she could transfer the file by explaining
the layers
Layer 7 - Application
Layer 6 - Presentation
Layer 5 - Session
Layer 4 - Transport
Layer 3 - Network
Layer 2 - Data Link
Layer 1 - Physical
HARDWARE AND LAYERS 1 & 2
Layer 7 - Application
Layer 6 - Presentation
Layer 5 - Session
LET’S EXPLORE
Layer 4 - Transport
Layer 3 - Network
Layer 2 - Data Link
Layer 1 - Physical
Layer 7 - Application
LAYER 1: PHYSICAL
•The network needs a physical channel through which it can move
bits of data between systems
 UTP Cables:
Layer 6 - Presentation
Layer 5 - Session
Layer 4 - Transport
Layer 3 - Network
Layer 2 - Data Link
Layer 1 - Physical
 Central Box:
• The cables lead to a central box
• Central box sends the data received from one system to all the other systems attached to it
• LAYER 1: defines the method of moving data between computers
• Anything that movies data from one system to another is in the OSI
Physical Layer
• Cables, fiber optics, radio waves
Layer 7 - Application
LAYER 1: EXAMPLE
Layer 6 - Presentation
Layer 5 - Session
Layer 4 - Transport
Layer 3 - Network
Layer 2 - Data Link
Layer 1 - Physical
The employee document can be sent from Janelle to Dana through cables and central hubs
Layer 7 - Application
LAYER 2: DATA LINK
• Network Interface Card (NIC): The
interface between the cables and the PCs
• Cables run from the NIC in the PC to a jack
on the wall or a hub
• Inside the wall another cable runs all the
way back to the central box
Layer 6 - Presentation
Layer 5 - Session
Layer 4 - Transport
Layer 3 - Network
Layer 2 - Data Link
Layer 1 - Physical
Layer 7 - Application
LAYER 2: DATA LINK
HOW DO NICs WORK?
• Each system (computer, device, etc.) needs
a unique identifier
•
Layer 5 - Session
Layer 4 - Transport
Layer 3 - Network
Layer 2 - Data Link
Layer 1 - Physical
Kind of like an address or telephone number to know
where the computer lives
• This is the Primary Job of the NIC
• The NIC has a chip that contains a media
access control address, or MAC Address
• MAC Address is ALWAYS unique
• Example:
• 00-40-05-60-7D-49
•
•
Layer 6 - Presentation
00-40-05 represents the NIC Manufacturer
Last six represent the serial number
The MAC address is printed on
the surface of the chip and
burned into the ROM chip:
004005-607D49
In computer terms:
00-40-05-60-7D-49
Layer 7 - Application
LETS LOOK UP OUR OWN MAC ADDRESS
Layer 6 - Presentation
Layer 5 - Session
Layer 4 - Transport
Layer 3 - Network
Click Start
Type cmd
Select the cmd application
Type ipconfig /all
Push enter
Your MAC Address is the physical address
Mine is 98-90-96-DD-30-E1
Layer 2 - Data Link
Layer 1 - Physical
Layer 7 - Application
LAYER 2: DATA LINK
INSIDE THE NIC: HOW ARE MAC Addresses Used?
• Computer data is binary
• NICs send and receive binary data as pules of
electricity, light, or radio waves
• Example:
•
•
electric charge (pulse) is a 1 and no pulse is a 0
Flash of light is 1 and no flash is a 0
• So…pulses represent binary data 1s and 0s
• But how does the network get the right data to the
right system?
• Frames!
Layer 6 - Presentation
Layer 5 - Session
Layer 4 - Transport
Layer 3 - Network
Layer 2 - Data Link
Layer 1 - Physical
Pulse
Pulse
3
Pulse
2
Pulse
Layer 7 - Application
LAYER 2: DATA LINK
INSIDE THE NIC: FRAMES!
• Networks transmit data by breaking down
whatever is moving across the physical layer
(files, web pages, print jobs, etc.) into chunks
called frames
• Frame: a container for a chunk of moving Sends to central box
across a network
• The NIC creates, sends, and receives this frame
Layer 6 - Presentation
Layer 5 - Session
Layer 4 - Transport
Layer 3 - Network
Layer 2 - Data Link
Layer 1 - Physical
Frame
I’m
building
a frame
Layer 7 - Application
LAYER 2: DATA LINK
INSIDE THE NIC: FRAMES CONT’D!
• A frame is made up of four general parts (see
below)
• Recipients MAC Address
• Sender’s MAC Address
• Type: specific network technology of the frame
•
(see https://en.wikipedia.org/wiki/Ethernet_frame#Ethernet_frame_types)
• Data: the actual data file, etc.
• frame check sequence (FCS): checks to see if
the frame is structured properly and can be
received and sent
Layer 6 - Presentation
Layer 5 - Session
Layer 4 - Transport
Layer 3 - Network
Layer 2 - Data Link
Layer 1 - Physical
Layer 7 - Application
LAYER 2: DATA LINK
HOW DO FRAMES GET TO THE RIGHT SYSTEM?
1.
When NIC sends frame, it goes into the central
box, or hub, or now in present-day called a
switch. The switch determines the next steps for
the frame
2. The switch stores information about the MAC
addresses in its central database. Using this data,
the switch determines whether the recipient
MAC Address exists on the network
3. If the MAC Address exists, the switch forwards
the data to the appropriate computer with the
correct MAC address
4. If the MAC Address does not exist, the switch
kills the transmission
Note: If the switch does not have the MAC Address
on file, it will send a mass broadcast to all computers
on the network asking them for their MAC addresses
Layer 6 - Presentation
Layer 5 - Session
Layer 4 - Transport
Layer 3 - Network
Layer 2 - Data Link
Layer 1 - Physical
Layer 7 - Application
LAYER 2: DATA LINK
THE COMPLETE FRAME MOVEMENT
1.
The operating system sends data to the NIC
2.
NIC builds a frame to transport the data
3.
NIC puts down the MAC access (recipient and its own) in the frame.
4.
Waits for the cable path to be clear
5.
Sends the frame through the cable to the network
6.
Frame goes down the cable as pulses to the hub or switch which creates
a copy of the frame and sends the frame to the correct MAC address
7.
If a MAC Address is found, the frame is sent. If not, the frame is erased.
8.
The NIC receives the frame
9.
The FCS verifies that the data is valid. If so, the NIC sends the data to the
software (the OS) to be processed.
Layer 6 - Presentation
Layer 5 - Session
Layer 4 - Transport
Layer 3 - Network
Layer 2 - Data Link
Layer 1 - Physical
Let’s Start on ICA#1